I have the Rode NT1-A mic, it's really good for the price. You'll need an audio interface with phantom power, though.

The audio software I use is Reason by Propellerheads. They have an audio interface, Balance (it does phantom power), that comes with an "Essentials"-only version of their software. That version doesn't have all the features, but it does record audio tracks just fine.

I am using Audacity to transfer my reel to reel and cassette tapes to my computer. It takes a little learning, but, so far, I love it.

For $99, you can't go wrong with the Shure SM58. But if you can go up to $129 you can get a mike more suited for the violin.

Small-Diaphram Cardiod mics on a budget:

Audio-Technica PRO 37 : This is a nice little mic and cheap, cheap, cheap. I bought mine for $99 (it’s a great live fiddle mic, and it’s super small, so I can keep it in my fiddle case and always have it on hand). Can be a little on the bright side, so some EQ might be necessary, but you could spend a lot more and get a lot less.

M-Audio Pulsar II: A good, neutral-sounding SDC in the same price range as the Pro 37.

Beyerdynamic MC903: This has a reputation for being the poor feller’s KM84, though it seems a little warmer, less bright than the Neumann KM84. Depending on the fiddle, I usually prefer it to the 84. Quality build, excellent sound.

Mic technique:

Finally, a word on where to put the mic. In the studio, fiddle players tend to go with an overhead mic positioned about 8-10 inches from the instrument. Beyond that point, use your ears. Some mics sound better right over the bow, others are better down the fingerboard. Some mics sound better on axis, others are better off axis. Sometimes it depends on the song.

I am using Audacity to transfer my reel to reel and cassette tapes to my computer. It takes a little learning, but, so far, I love it.

...so some EQ might be necessary, but you could spend a lot more and get a lot less.

Beyerdynamic MC903: This has a reputation for being the poor feller’s KM84, though it seems a little warmer, less bright than the Neumann KM84.

Yeah, you can use Audacity to do a lot of things. But once you use a program actually designed for musicians, and not computer programmers (and this is coming from a computer guy), you'll never want to touch that thing again. It's horribly obtuse to get anything done that you'd actually want when just trying to jam, and get a recording of it.

As for mics with less than linear response, as long as the noise floor is low enough, you can totally change the character with an EQ. So don't worry about "bright" or "dull" in reviews, all you need to do it throw a parametric EQ on insert effect chain, and voila (not viola).

There are mics that have a USB cable, are their own sound card*, and pull the phantom power from there. But I've never seen one that was really recommended for recording instruments. They are all targeted at podcasters, and recording speaking voice.

Yeah, a USB mic can get you started for cheap, but expect to throw it away if you want to progress any further than recording a single track without monitoring.

*There's another problem with this, USB mics are a soundcard with just an input and no output. This is fine for Windows sounds, but if you end up using a more professional piece of audio software, it is highly recommended that all the inputs, and outputs are on the same interface. The biggest problem is latency for monitoring. If the audio is going into the mic's interface, being processed by the computer, and re-output from another interface, there's no way to minimize the round trip time (professional audio interfaces have local monitoring, that sidesteps the computer completely), and what you hear in the monitors (headphones) is delayed enough that it makes it difficult to play/sing correctly. The other less noticeable problem is clock skew, but that only really applies to combining the input from multiple interfaces into one recording.